I have 3 of these scattered throughout my house -
http://www.amazon.com/UPGRADED-Wirel...dp/B00C40OG22/
The surface is non-slip and 2 of the 3 pads charge reasonably quick. One of them has always charged relatively slowly, however. But....I just noticed when I looked at the Amazon listing that it needs at least 2 amps, and the USB adapter I have in the problem location is just a single amp.